The present invention relates to methods for producing high quality laser-induced images in transparent objects using high power laser radiation creating laser-induced color centers on basis of photolonization and laser-induced damages on basis of the breakdown phenomenon.
A number of techniques for creating a variety of patterns on the surface and inside of transparent substrates using pulsed laser radiation are well known.
One publication disclosing such techniques is the Russian invention # 321422 to Agadjanov et. al., published on Nov. 16, 1970 (#140454529-33). The invention concerns a method of manufacturing decorative products inside a transparent material by changing the material structure by laser radiation. As disclosed, by moving a material relative to a focused laser beam, it is possible to create a drawing inside the material.
U.S. Pat. No. 3,715,734 to Fajans discloses a three-dimensional memory storage unit, which is prepared by carbonizing selected spots in a block of polymethylmethacrylate by means of a steeply converging laser beam. The energy of the beam is applied in pulses of such duration and at such intensity that carbonization takes place only at the focal point of the beam.
U.S. Pat. No. 4,092,518 to Merard discloses a method for decorating transparent plastic articles. This technique is carried out by directing a pulsed laser beam into the body of an article by successively focusing the laser beam in different regions within the body of the article. The pulse energy and duration is selected based upon the desired extent of the resulting decorative pattern. The effect of the laser is a number of three dimensional xe2x80x9cmacro-destructionxe2x80x9d (fissures in the material of the article) appearing as fanned-out cracks. The pattern of the cracks produced in the article is controlled by changing the depth of the laser beam focus along the length of the article. Preferably, the article is in the form of a cylinder, and the cracks are shaped predominantly as saucer-like formations of different size arranged randomly around the focal point of the optical system guiding a laser beam. The device used to carry out this technique is preferably a multi-mode solid-state, free-running pulse laser used in conjunction with a convergent lens having a focal length from 100 to 200 mm.
GDR Patent No. 237 972 A3 to Wiederhold et al, discloses an opaque image pattern imbedded within the inner volume of an otherwise transparent article, without surface damage, using a focused, guided laser with an intensity (power density) at the focal area that exceeds the damage threshold. For instance, to create internal marks in a material having a damage intensity threshold of 40 kW/mm2 which is achievable with an average peak power of 20 kW, a laser with a 2,5 time higher peak power (50 kW) is employed, implying conditions under which ionization is reached.
U.S. Pat. No. 4,843,207 to Urbanek et al., discloses a method of creating controlled decorations on the surface of a hollow symmetrical transparent article. This technique is preferably carried out on glass. The glass is preconditioned with a coating on the outer surface of the glass being approximately 1.2 mm thick and made of a material having at least 75% absorption of laser radiation. The technique is also carried out using a laser having a wave of length of 0.5 to 2 microns acting upon the external coating through the wall of the cylindrical glass article. The laser beam moves so that it is focused on the surface of the cylinder, and moves about the axis of symmetry of the cylinder to irradiate the aforementioned surface coating. As a result, the irradiated portions of the surface coating go through a phase change and a pattern is formed.
U.S. Pat. No 5,206,496 to Clement et al. discloses a method and apparatus for providing in a transparent material, such as glass or plastic, a mark which is visible to the naked eye or which may be xe2x80x9cseenxe2x80x9d by optical instruments operating at an appropriate wavelength. The Clement et al. Patent describes a method and apparatus for producing a subsurface marking which is produced in a body such as bottle, by directing into the body a high energy density beam and bringing the beam to focus at a location spaced from the surface, so as to cause localized ionization of the material. In the preferred embodiment the apparatus includes a laser as the high energy density beam source. The laser may be a Nd-YAG laser that emits a pulsed beam of laser radiation with a wavelength of 1064 nm. The pulsed beam is incident upon a first mirror that directs the beam through a beam expander and a beam combiner to a second mirror. A second source of laser radiation in the form of a low power He-Ne laser emits a secondary beam of visible laser radiation with a wavelength of 638 m. The secondary beam impinges upon the beam combiner where it is reflected toward the second reflecting surface coincident with the pulsed beam of laser radiation from the Nd-YAG laser. The combined coincident beams are reflected at the reflecting surface via reflecting two other surfaces to a pair of movable mirrors for controlling movement of the beam. The beam then passes through a lens assembly into the body to be marked.
Soviet patent publication 1838163 to P. V. Agrynsky, et. al discloses a process for forming an image in a solid media by processing of the optically transparent solid material by a beam of radiation with changeable energy for creation of the image.
WIPO Patent Document No. 96/30219 to Lebedev discloses a technology for creating two- or three-dimensional images inside a polymer material using penetrating electromagnetic radiation. The technology can be used for marking and for producing decorative articles and souvenirs. Specifically, laser radiation is used as the penetrating radiation, and carbonizing polymers are used as the polymer material. By these means, it is possible to produce both black and half-tone images in the articles.
U.S. Pat. No 5,268,862 to Rentzepis et al. discloses a method for creating three-dimensional optical memory by two UV laser light beams, typically of 532 nm. and 1064 nm. Wavelength, to change from a first, spiropyran, to a second, merocyanine, stable molecular isomeric form by process of two-photon absorption.
U.S. Pat. No. 5,575,936 to Goldfarb discloses a process and apparatus where a focused laser beam causes local destruction within a solid article, without effecting the surface thereof The apparatus for etching an image within a solid article includes a laser focused to a focal point within the article. The position of the article with respect to the focal point is varied. Control means, coupled to the laser, and positioning means are provided for firing the laser so that a local disruption occurs within the article to form the image within the article.
U.S. Pat. No 5,637,244 to Erokhin discloses a technique which depends on a particular optical system including a diffraction limited Q-switched laser (preferably a solid-state single-mode TEM00) aimed into a defocusing lens having a variable focal length to control the light impinging on a subsequent focusing lens that refocuses the laser beam onto the transparent article being etched. The laser power level, operation of the defocusing lens, and the movement of the transparent article being etched are all controlled by a computer. The computer operates to reproduce a pre- programmed three-dimensional image inside the transparent article being etched. In the computer memory, the image is presented as arrays of picture elements on various parallel planes. The optical system is controlled to reproduce the stored arrays of picture elements inside the transparent material. A method for forming a predetermined half-tone image is disclosed. Accordance to the method, microdestructions of a first size are created to form a first portion of the image and microdestruction of a second size different from the first size are created to form a second portion of the image. Different sizes of microdestructions are created by changing the laser beam focusing sharpness and the radiation power thereof before each shot.
U.S. Pat. No. 5,653,900 to Clement, et al. discloses a method and an apparatus for making a moving body of material. In a preferred embodiment, the apparatus includes at least one movable galvanometer mirror capable of moving the laser beam to create a mark of a predetermined shape.
U.S. Pat. No 5,656,186 to Mourou, et al. discloses a method for controlling configuration of laser induced breakdown and ablation. The method comprises generating a beam of laser pulses in which each pulse has a pulse width equal to or less than the predetermined laser pulse width value. The beam is focused to a point at or beneath the surface of a material where laser induced breakdown is desired. The technique can produce features smaller than the spot size and Rayleigh range due to enhanced damage threshold accuracy in the short pulse regime.
U.S. Pat. No 5,786,560 to Tatah et al. discloses a method of treating a material by generating an ultraviolet wavelength laser beam having femtosecond pulses; splitting the laser beam into a plurality of separate laser beams; directing these laser beams onto a target point within a sample such that the beams overlap to create an intensity sufficient to treat the sample.
U.S. Pat. No. 5,886,318 to A. Vasiliev and B. Goldfarb discloses a method for laser-assisted image formation in transparent specimens, which consists in establishing a laser beam having different angular divergence values in two mutually square planes. An angle between the plane with a maximum laser beam angular divergence and the surface of the image portion being formed is changed to suit the required contrast of an image.
EPO Patent Document 0743128 to Balickas et al. disclose a method of marking products made of transparent materials which involves concentration of a laser beam in the material which does not absorb the beam, at a predetermined location, destruction of the material by laser pulses and formation of the marking symbol by displacement of the laser beam. Destruction of the material at that location takes place in two stages. In the first stage, the resistance of the material to laser radiation is altered, while, in the second stage, destruction of the material takes place at that location.
Russian patent publication RU 20082288 to S. V. Oshemkov discloses a process for laser forming of images in solid media by the way of focusing of laser radiation in a point inside a sample which differs by following: with the aim to save the surface and the volume of the sample before the definite point and creation of three dimensional images, the sample is illuminated with the power density higher than the threshold of volume breakdown and moving the sample relatively to the laser beam in three orthogonal directions.
U.S. Pat. No. 6,087,617 to Troitski et al. discloses a computer graphic system for producing an image inside optically transparent material. An image reproducible inside optically transparent material by the system is defined by potential etch points, in which the breakdowns required to create the image in the selected optically transparent material are possible. The potential etch points are generated based on the characteristics of the selected optically transparent material. If the number of the potential etch points exceeds a predetermined number, the system carries out an optimization routine that allows the number of the generated etch points to be reduced based on their size. To prevent the distortion of the reproduced image due to the refraction of the optically transparent material, the coordinates of the generated etch points are adjusted to correct their positions along a selected laser beam direction.
U.S. Pat. No. 6,333,485 to Haight, et al. discloses a method for minimizing sample damage during the ablation of material using a focused ultra short pulse beam. The beam is focused above the surface of a material where laser induced breakdown is desired. The region of least confusion (minimum beam waist or average spot size) is above the surface of the material in which laser induced breakdown is desired since the intensity of the beam falls in the forward direction.
U.S. Pat. No. 6,333,486 B1 to Troitski discloses method and laser system for creation of laser-induced damages to produce high quality images. Accordance to the invention, a laser-induced damage is produced by simultaneously generating breakdowns in several separate focused small points inside the transparent material area corresponding to this etch point. Damage brightness is controlled by variation of a number of separate focused small points inside the transparent material area.
U.S. patent application Ser. No. 09/583,454 to Troitski discloses method and laser system controlling breakdown process development and space structure of laser radiation for production of high quality laser-induced damage images. Accordance to the invention, at the beginning an applied laser radiation level just exceeds an energy threshold for creating a plasma condition in the material, and thereafter the energy level of the applied laser radiation is just maintain the plasma condition. Accordance to another method a laser generates a TEMmn. radiation. The values of the integers m and n are controlled and determined so as to reproduce particular gray shades for a particular point of an image.
U.S. patent application Ser. No. 09/613,296 to Troitski discloses method and laser system for producing high quality laser-induced damage images by using material processing made before and during image creation.
The experiments described in a publication entitled xe2x80x9cPhotoionization of silicate glasses exposed to IR femtosecond pulsesxe2x80x9d (O. M. Efimov et al., Journal of Non-Crystalline Solids 253 (1999), 58-67) show that photoionization of silicate glasses is possible under infrared (IR) high-power femtosecond (about 100 fs) pulses, and color centers are generated by laser pulses at irradiance below the thresholds of laser-induced damage and catastrophic self-focusing.
The publication xe2x80x9cSystem for creation of laser-induced damage images and problems of their optimizationxe2x80x9d (I. N. Troitski, Proc. of SPIRE Vol. 3902 (2000), 489-499) describes methods for generating 3D images and portraits allowing reproduction of them within an optically transparent material with the same resolution like computer images, without sharp point structure and without significant fluctuation of gray shades.
The publication xe2x80x9cExperience of creation of laser-induced damage imagesxe2x80x9d (I. N. Troitski, Proc. of SPIE Vol. 3902 (2000), 479-488) discloses the specific system for production of laser-induced damage images. The publication xe2x80x9cImage recording by laser-induced damagesxe2x80x9d (I. N. Troitski, Optical Memory and Neural Networks, Vol. 9, No. 4, (2000) 233-238) discusses the problems of laser-induced damage utilization for image recording.
The publication xe2x80x9cLaser-induced color centers in silicaxe2x80x9d (Linards Skuja,et al., SPIE Volume 4347 (2000) 155-167) reviews the color centers contributing to the optical absorption spectrum of synthetic silica glass in the near infraredxe2x80x94to vacuum UV range. The optical properties of common impurities/dopants in synthetic silicas used in laser optics are discussed.
The present invention has its principal task to provide a method for production of unique laser-induced images based on areas of laser-induced color centers and laserinduced damages.
One or more embodiments of the invention comprise a method for division of computer image pixels into two arrangements: the first includes pixels, which should be produced by the areas of color centers, the second arrangement contains pixels, which should be produced by laser-induced damages.
One or more embodiments of the invention comprise a method for generation of UV radiation inside the predetermined area of the material, which is opaque for UV radiation but is transparent for IK light, by focusing IK ultra short (from femtosecond to picosecond) laser pulsed radiation into this area.
One or more embodiments of the invention comprise a method for producing laser-induced images using color centers created by light radiation with broadened spectral, which is generated by IK ultra short (from femtosecond to picosecond) laser pulsed radiation focused into predetermined area.
One or more embodiments of the invention comprise a method for producing laser-induced images containing color centers and laser-induced damages by the laser generating IK ultra short (from femtosecond to picosecond) pulses with operated energy.
One or more embodiments of the invention comprise a method for producing the single-layer laser-induced image rendering all pixels of corresponding computer image by creating the arrangement of laser-induced damages and the laser-induced color centers, which are located in immediate proximity to laser-induced damages and which reproduce all missing pixels, which can not be produced by laser-induced damages.
One or more embodiments of the invention comprise a method for producing several different laser-induced images inside the same transparent material so that each of them is visible inside its small space angle.